Cation exchange membrane and method of making same

ABSTRACT

A cation exchange membrane comprising a membranous insoluble, infusible organic high-molecular-weight polymer having cation exchange groups chemically bonded thereto and having the dimension of at least 1 centimeter in two directions, the substantial surface of said membrane being chemically bonded with acid amide bonds in a proportion such that the percentage indicated by the following equation is satisfied: A/(A+B) X 100 15-10 5% wherein A is the number of acid amide bonds per gram of dry membrane and B is the number of cation exchange groups per gram of dry membrane, SAID ACID AMIDE BONDS BEING COMPOSED OF A CATION EXCHANGE GROUP AND AN AMINE HAVING ONE AMINO GROUP CONTAINING AT LEAST ONE HYDROGEN ATOM BONDED TO A NITROGEN ATOM AND A METHOD OF MAKING THE SAME.

United States Patent Mizutani et al.

[ 1 Mar. 7, 1972 CATION EXCHANGE MEMBRANE AND M THOD OF MAKING sAMEYukio Mizutani; Reiichi Yamane; Toshikatsu Sata, all of Tokuyama-shi;Ryuii lzuo, Kudamatsu-shi, all of Japan Tokuyama Soda Kabushiki Kaisha,

Tokuyama-shi, Japan Filed: July 9, 1969 Appl. No.: 1 840,513

Inventors:

Assignee:

US. Cl...... ..2 l0/500, 204/296, 260/22 Int. Cl 1 ..-......B0ld 39/16Field of Search ..2i0/22, 23, 321, 500;

References Cited UNITED STATES PATENTS 10/1 966 Nishihara et al..204/296 2/1968 Kohn et al. ..260/2.2 6/1968 Korosy et al. ..204/296 xMizutani et al. ..204/1 80 P X Primary Examiner-Frank A. Spear, Jr.

Attorney-Sherman and Shalloway 57 ABSTRACT I wherein A is the number ofacid amide bonds per gram of dry membrane andB is the number of cationexchange groups per gram of dry membrane, said acid amide bonds beingcomposed of a cation exchange group and an amine having one amino groupcontaining at least one hydrogen atom bonded to a nitrogen atom and amethod of making the same.

11 Claims, No Drawings CATJON EXCHANGE MEMBRANE AND METHOD OF MAKINGSAME This invention relates to a cation exchange membrance having theproperty of selectively effecting the permeation of cations of smallervalence from a solution containing two or more classes of cations ofdiffering valence, and to a method of making same. More particularly,the invention relates to a cation exchange membrane havingpermselectivity between cations, characterized by having acid amidebonds in its surface or neighborhood of its surface (hereinafter thissurface inclusive of its neighborhood being referred to as thesubstantial surface); and to a method of making same.

It has been known in the past to effect the separation of acid or base,concentration of salt water, desalting or the double decomposition byusing the ion exchange membrance. In these cases, the ion exchangemembranes (usually referred to respectively as the cation exchangemembrance and the anion exchange membrane) which have the property ofeffecting the selective permeation of the cations and anions are usedeither independently of each other or in combination.

As ion exchange membranes which can stand commercial use, therequirement is that they have low electric resistance, the transportnumber of the ions whose transport through the membrane is desired isgreat and the strength, and especially the dimensional stability, of themembrane itself is great. The various cation exchange membranes whichhave been proposed for commercial use in the past can be classified asfollows:

a. The nonhomogeneous ion exchange membrane. A mixture of a cationexchange resin powder and a thermoplastic powder formed into membraneform. For example, those disclosed in U.S. Pat. Nos. 2,681,319,2,681,320 and 2,827,426, British Patent specification No. 810,391, andJapanese Patent applications Publication Nos. 9477/1957 and 7720/1959.

b. lnterpolymer membranes (casting membranes). Those obtained bydissolving polystyrene sulphonic acids in a solvent such as water,alcohol or dimethylformamide and dissolving therein ahigh-molecular-weight substance soluble in said solvent to become thereinforcing material, such, for example, as polyvinyl alcohol, vinylchloride-acrylonitrile copolymer or collodion, and casting this solutiononto a flat surface and thereafter evaporating the solvent and strippingthe remaining film, and in the case the resulting film is one which issoluble insolubilizing it by cross-linking. For example, those disclosedin J. Phys. Chem. 58, 916-925 (1954), ibid. 61, 141 (1957), ibid. 61,147-151 (1957); Discussions of Faraday Soc. 21, 162 (1956); and BritishPat. specification No. 835,137.

c. Soaking process membranes. Those obtained by dipping a film such asof polyvinyl chloride, polyethylene, polypropylene and fluorine resinsin a vinyl monomer or a vinyl monomer containing a cross-linking agentand, after the film has been thoroughly impregnated with the monomer,polymerizing it by radical, thermal, radiation or ionic polymerizationand thereafter introducing an ion exchange group into the film. Forexample, those disclosed in the J. Polymer Sci. 23, 903-913 (1957);Denki Kagaku (The Electrochemical Society of Japan) 30, 335-337 (1962);Research Reports of Asahi Glass Company, Japan, 10, 117-128 (1960); andJapanese Pat. application Publication No. 4590/1957.

d. Membranes made from monomers having functional groups which can bechanged readily to ion exchange groups. Those obtained by mixing across-linking agent such as divinylbenzene and divinylsulfonehomogeneously with a vinyl monomer having a functional group which canbe changed readily to an ion exchange group, such as the esters of vinylmonomers containing an exchange group (e.g., vinyl sulfonic acid esters,styrene sulfonic acid esters, methyl methacrylate and methyl acrylate)or vinyl sulfonyl chloride, then bulk polymerizing the resultingmonomeric vinyl mixture using a radical initiator, after which theresulting polymer is made into membrane form and hydrolyzed to obtainthe ion exchange membrane. For example, those disclosed in German (East)Pat. No. 18357 (1960), J. Phys. Chem. 59 No. 1, 86-89 (1955), Can, J.Chem. 32, 143 (1954) and Journal ofChemical Society ofJapan 62,1929-1934 (1959).

e. After-treated membranes (cation exchange membranes obtained byintroducing an ion-exchange group into a membrane high-molecular-weightpolymer into which an ionexchanging group is capable of beingintroduced) i. Cation exchange membranes obtained by the directchlorosulfonation of sheets of such as polyvinyl chloride, polyethylene,and polypropylene with chlorosulfonic acid or by exposure to ultravioletradiation using a gas mixture of S0 and C1 followed by submitting thesheets to hydrolysis. For example, those disclosed in German Pat. No.1,001,669, U.S. Pat. No. 2,948,637, Dutch Pat. No. 81298, and U.S. Pat.Nos. 2,767,575 and 2,858,264.

ii. Those obtained by mixing and dissolving a linearhighmolecular-weight substance such as polystyrene and natural rubberwith either styrene, divinylbenzene, dioctyl phthalate or benzoylperoxide, heating and polymerizing this mixture to obtain a lumpyhigh-molecular-weight polymer, and thereafter cutting this polymer intothin pieces followed by a sulfonation treatment. For example, thosedisclosed in Japanese Pat. applications Publication Nos. 4142/1957,4144/1957, 10696/1957, 2645/1958, 3892/1958, 5740/1958 and 7290/1960.

iii. Those obtained by dipping a glass fiber cloth or polyester cloth ina styrene-butadiene copolymer latex, after which the cloth is withdrawnand air-dried, followed by sulfonation with, say, 95% H directly orafter treating the impregnated cloth with either SnCL, or TiCl.,. Forexample, those disclosed in Japanese Pat. applications publication Nos.13009/1960 and 4210/1961.

iv. Those obtained by mixing a mixed monomer solution predominantly of amonomer having a functional group suitable for the introduction of anion exchange group with a finely divided, thermoplastichigh-molecularweight substance to yield a pasty product, which is fonnedinto film' and polymerized, after which ion exchange groups areintroduced thereinto. For example, those disclosed in Japanese Pat.applications publication Nos. 19542/1964 and 28951/1965.

It is also proposed that for further augmentation of the mechanicalstrength of the hereinabove described cation' exchange membranes atextile substance of net, fabric or yarn form be applied as areinforcing material wherever possible.

However, since there was practically no perms'e'lectivity between thecations in the case of the conventional ion exchange membranes, it wasnot possible to permit the passage of only those cations which wereparticularly wanted. Attempts have been made to improve upon thisdrawback by developing a cation exchange membrane havingperrnselectivity between the cations. These attempts can be classifiedas follows:

1. An ion exchange membrane of high cross-linked resin structure. [Forexample, that disclosed in Denki Kagaku 27, 482 1959)] 2. A cationexchange resin membrane whereon has been formed a thin film of condensedhigh cross-linked resin [For example, those disclosed in Denki Kagaku29, 544 (1961 and Japanese Pat. applications publication Nos. 3164/1961,4210/1961 and 6647/1963] 3. An ion exchange membrane containing bothanion and cation exchange groups. (For example, that disclosed inJapanese Pat. application publication No. 943/1960) 4. A membrane madeup of a lamination of an anion exchange membrane and a cation exchangemembrane. [For example, that disclosed in the Journal of AppliedChemistry 6, 511 (1956)] 5. An ion exchange membrane having a specialexchange group, i.e., a phosphoric acid group. (For example, thatdisclosed in Japanese Pat. application publication No. 531/1965) Theforegoing attempts cannot be regarded as being fully establishedtechniques in view of the following shortcomings: the membrane describedin (1), above, has a high electric resistance, whereas that of (2) ispoor in its durability. In the case of the membrane of (3), thepermselectivity between the cations is not only poor but its transportnumber of cation is also low. In addition, its electric resistance ishigh and its transport number is low. In the case of the membrane of(4), not only is the electric resistance high but also a satisfactorymethod of carrying out the lamination of the membranes is not known. Onthe other hand, in the case of the membrane of (5), the membrane becomescostly since the exchange group is limited to the phosphoric acid typeand, in addition, its I permselectivity between cations isdisappointing. Hence, the demand in the art is for a cation exchangemembrane having a much more superior permselectivity between ions of thesame sign.

An object of the present invention is to provide an ion exchangemembrance which can effect the permeation selectivity of differentclasses of cations, and particularly cations whose valence is small.

Another object resides in making by a very simple procedure a cationexchange membrane which has the ability to effect the permeationselectivity of cations and which moreover excels in its durability.

A further object is to provide a cation exchange membrane which caneffect the permeation selectivity of particularly the cations of smallervalence from among the different classes of cations and, in addition,whose transport number of these cations of smaller valence is great aswell as whose electric resistance is small.

Other objects and advantages of the invention will become apparent fromthe following description.

A cation exchange membrane is provided according to the presentinvention which is characterized in being a membranous insoluble andinfusible organic high-molecular-weight polymer having cation exchangegroups chemically bonded thereto and having the dimension of at least 1centimeter in at least two directions, the substantial surface of saidmembrane being chemically bonded with acid amide units in an amountindicated by the expression A/A+B lO=l5l0 I wherein A is the number ofacids amide bonds in 1 gram of the dry membrane and B is the number ofcation exchange groups in 1 gram of the dry membrane,

said acid amide units being composed of an amine having at least oneamino group containing at least one hydrogen atom bonded to a nitrogenatom and a cation exchange group. The expression A/A+B X 100 willhereinafter be referred to at times as the percent acid amide bonds.

There is no particular restriction as to the cation exchange group thatis present in the cation exchange membrane of the present invention aslong as it is one possessing a cation exchange capacity. Thosepreferred, however, are the sulfonic acid, carboxylic acid andphosphoric acid groups, and from the standpoint of economy the sulfonicacid group is most preferred.

Further, in general, the number of sulfonic acid, carboxylic acid andphosphonic acid groups, and other cation exchange groups, that isintroduced into the membrance as cation exchange groups, i.e., theexchange capacity, varies depending upon the class of the exchange groupas well as the class of the resin. Generally speaking, when the numberof cation exchange groups in the membrane is too great, the mechanicalstrength is decreased and, on the other hand, when it is too small, theelectric resistance of the cation exchange membrane increases andmoreover the permselectivity between. ions of different signs becomelower. In the invention cation exchange membrane usually the number ofcation exchange groups is most suitably within the range of 0.5-6.0milliequivalent per gram of the dry membrane (hereinafter will beabbreviated to meq./g. dry memb.).

in the invention cation exchange membrane the matrix of organichigh-molecular-weight polymer having chemically bonded thereto thehereinbefore described cation exchange group is imposed no particularrestriction as long as it is insoluble and infusible under theconditions of its use as an ion exchange membrane, and hence it may beany resin which meet these requirements. As such a polymeric matrix, thesynthetic resin matrices mentioned in (a) to (e), above, which per 'seare know, can be used. Particularly convenient for achieving the objectsof the present invention are the aforementioned resin matrices of (d)and (e), above.

An important feature of the present invention resides in the fact thatthe cation exchange membrane has bonded to its substantial surface acidamide units composed of an amine having at least one amino groupcontaining at least one hydrogen atom bonded to a nitrogen atom and theaforesaid cation exchange groups, the amount of the acid amide unitsbonded being at the rate of 15-10 percent based on the number of thecation exchange groups plus the number of the acid amide groups. That isto say, we found that when the acid amide units are chemicallyintroduced to the substantial surface of the cation exchange membranethe acid amide units impart to the cation exchange membrane a propertywhich makes it possible for it to effect the permeation selectivity ofthe cations of smaller valence and that this permselectivity lasts for asurprisingly long period of time. Further, it was found that the cationexchange membrane having these acid amide units bonded in an amountwithin the range specified by the present invention 'had a much smallerelectric resistance than the conventional perrnselective ion exchangemembranes, i.e., aforesaid membranes of l5 and, in addition, wascharacterized in that its transport number of the cations of smallervalence was exceedingly great. Furthermore, since in the case of theinvention cation exchange membrane it is chemically bonded with aminecompounds having a primary or secondary amino group, it is usuallypossible to use a lesser amount of the aforesaid compound having theamino group than in the case of a cation exchange membrance comprisingthe conventional cation exchange membrance to which the aforesaidcompound has just merely been absorbed (including the ionic bond andhereinafter referred to simply as an absorbed membrane). In addition,the invention cation exchange membrane demonstrates a much more superiorpermselectivity for the cations of smaller valence and is alsooutstanding in its durability.

When the proportion of the acid amide units is less than 1X10 percent,the permselectivity for the cations of smaller valence is low, whereasthis proportion exceeds 15 percent, not only the electric resistancerises but the transport number decreases as well. While the mostconvenient proportion for the acid amide units in this invention willvary depending upon the class and molecular weight of amines used in theacid amide bond, it is usually in the range between l0 percent and 10percent.

While the amines used in the acid amide bond may be those having atleast one amino group containing at least one hydrogen atom bonded to anitrogen atom, usually used are those having a molecular weight of atleast 60, and particularly preferred are those whose molecular weightexceeds 200.

As these amines, included are the following:

i. Compounds of the formula wherein R and R are each hydrogen with thelimitation that when one is hydrogen, the other is not; alkyl,haloalkyl; alkyl substituted by either hydroxy, carboxy, alkoxy,phosphonic acid, sulfonic acid, nitro, nitrile, carbamoyl, sulfonic acidamide or phosphonic acid amide; aryl; aryl substituted by hydroxy,carboxy, phosphonic acid, alkoxy, sulfonic acid, nitro, nitrile,carbamoyl, sulfonic acid amide, carbamoyl or phosphonic acid amide; aheterocyclic group; or aralkyl.

Examples:

diethylamine, butylamine, octylamine, nonylamine, decylamine,dodecylamine, octadecylamine,

ethanolamine, diethanolamine, aminopyridine, aniline, nitroaniline,phthalimide, aminobenzophenone, aminosalicylic acid, amino acids,aminonaphthalene-sulfonic acids, amino phenols, aminobenzoic acids,aminonaphthalenes, perfluoro hexylamine and perfluoro laurylamine.

ii. Compounds of the formula wherein R,,, R and R are each hydrogen,alkyl or aryl, R and R are each alkylene, and n is a number 0 or 1 ormore.

Examples: ethylene diamine, diethylene triamine, triethylene tetraminetetraethylene pentamine, tetraethylene diamine, triethylene diamine,polyethyleneimine and iv. Polymer having repeating units of the formulawherein R is hydrogen or alkyl, R is alkylene or phenylene, and m is 0or 1. Examples: polyvinylamine and the N-alkyl derivatives thereof,polyaminostyrene and the N-alkyl derivatives thereof, and polyallylamineand the N-alkyl derivatives thereof. v. Dyestuff or dyestuff base havingat least one primary or secondary amino group.

Examples: indamines, phenylene blue, safranine, oxazine, Bismarck brown,Auramine conc., magenta and glycidine crystals. The amines which areparticularly effective for achieving the objects of the presentinvention are those of (iii.) and (iv.), above, e.g., polyethyleneimine,polyvinylamine, polyaminostyrene and polyallylamine. When these aminesare used, it becomes possible to fully develop the permselectivity forcations of smaller valence even in those cases where the percent acidamide bonds present in the surface of the cation exchange membrane is ina relatively small amount of IO I percent.

While the invention cation exchange membrane will do with a size whichis at least 1 centimeter in at least two directions, one whose thicknessranges 0.01-1 centimeter, and particularly 0.0l-O.2 centimeter, can beused most economically from the commercial standpoint. If the thicknessof the cation exchange membrane becomes thicker than the above-indicatedrange, while there is the advantage that the mechanical strengthgenerally becomes greater and the ions that escape on account of thediffusion phenomenon decrease, the electric resistance of the membraneincreases, with the consequence that its usefulness suffers. On theother hand when the thickness of the aforesaid cation exchange membraneis less than the range specified above, unfavorable results are broughtabout in that there is an increase in the escape of ions during use dueto the diffusion phenomenon and there is a marked decline in themechanical strength, thus being undesirable from the economicalstandpoint.

The foregoing cation exchange membrane of the present invention havingcation exchange groups and acid amide units chemically bonded theretocan be made by reacting a membrane of an insoluble and infusible organichigh-molecularweight polymer having chemically bonded thereto reactivegroups selected from the class consisting of the sulfonic acid halidegroups, carboxylic acid halide group, phosphoric acid halide groups andcarboxylic acid anhydride groups, with an amine having at least oneamino group containing at least one hydrogen atom attached to a nitrogenatom, in a proportion such that the percentage specified by thefollowing equation is satisfied:

A/A+BXI00=I510' (I) wherein A is the number of acid amide bonds per gramof dry membrane and B is the number of cation exchange groups per gramof dry membrane; and thereafter treating the resulting membrane with anaqueous alkaline solution to hydrolyze said remaining reactive groups tocation exchange groups.

In making the invention cation exchange membrane, the method ofintroducing the reactive groups of acid halide groups or carboxylicanhydride units to the matrix of insoluble and infusiblehigh-molecular-weight organic polymer is not particularly restricted andthe methods which per se are known can be employed.

The foregoing insoluble and infusible organic high-molecular-weightpolymer having reactive groups chemically bonded thereto can be formedby polymerizing an alpha, betaethyleneically unsaturated monomer havingthe aforesaid acid halide groups or acid anhydride groups, in thepresence of other alpha, beta-ethylenically unsaturated monomers, alongwith an initiator and a crosslinking agent such as divinylbenzene ordivinylsulfone. For example, a membrane of a polymer having the acidanhydride units is formed by the radical polymerization of maleicanhydride or itaconic anhydride with a monomer such as styrene ormethacrylic acid, and divinylbenzene. In this case, a thermoplasticresin powder such as polyvinyl chloride, polyvinyl acetate andpolyethylene can be incorporated in an amount, say, of up to percent byweight of the total weight prior to the polymerization to render thewhole into a paste, after which this paste is applied to a substrate,e.g., net or textile fabric or cloth, to form a film which is thenpolymerized.

Again, a powder of a polymer containing in advance the acid halidegroup, such as polyethylene halosulfonate, can be admixed with astyrene/divinylbenzene monomeric mixture, after which this mixture ispolymerized with an initiator to convert the whole into an insoluble andinfusible organic highmolecular-weight membrane.

Alternatively, a membrane of a polymer not containing the cationexchange groups, such as styrene-divinylbenzene copolymer, styrene-vinylether-divinylbenzene copolymer,

, styrene-butadiene copolymer and styrene-methacrylic ester- Thestarting membrane, i.e., the insoluble and infusible or- "anichighimolecular-weight polymeric membrane, to be used in the presentinvention can also be made by using the commercially available cationexchange membranes. For example, in using the known cation exchangemembrane having the carboxylic acid type of cations as the startingmembrane in this invention, the foregoing membrane is reacted withphosphorus halide or thionyl chloride and either all or part of theforegoing carboxylic acid groups are converted to a carboxylic acidhalide.

On the other hand, when using the commonly known cation exchangemembrane having the sulfonic acid type cation as the starting membranein this invention, the cation exchange groups of the foregoing sulfonicacid type cation exchange membrane are converted to alkali metal saltsand then by reacting these with either phosphorus pentahalide orphosphorus oxyhalide the starting membrane is made into one having ahalosulfonic acid group by the introduction thereinto of thehalosulfonic acid groups.

Further, in the case where the commonly known cation exchange membraneshaving the phosphoric acid type cations are used as the startingmembrane in this invention, the aforesaid membrane is either reactedwith phosphorus halide in the presence of a Friedel-Crafts catalyst tointroduce the phosphorus halide groups thereinto, or the membrane, afterhaving been chloromethylated, is reacted with phosphorus halide therebyintroducing the phosphorus halide groups thereinto.

According to this invention, the starting membrane having the acidhalide groups or carboxylic anhydride units is reacted with thepreviously described amines. it is extremely important to ensure thatthe reaction between the amines and the acid halide groups or carboxylicanhydride units takes place in such a manner that the formation of theacid amide bonds occurs only at the substantial surface of the startingmembrane. The reason is that when the aforesaid acid amide bond proceedsto the interior of the cation exchange membrane not only the transportnumber of the resulting cation exchange member declines and also itselectric resistance demonstrates a marked increase but also, in extremecases, its capacity to function as a cation exchange membrane is lost,with the consequence that the achievement of the objects of the presentinvention becomes impossible.

In the present invention the formation of the acid amide bonds in theinterior of the cation exchange membrane can be avoided by ensuring thatthe amount of amine reacted with the acid halide group or the carboxylicanhydride unit with respect to the acid amide bond formed with thecation exchange group (the unreacted acid halide group or carboxylicanhydride unit becomes a cation exchange group by the next followinghydrolysis) becomes a proportion indicated by the previously givenequation l The reaction for forming the acid amide bond can be carriedout either by dipping the membrane having the acid halide or carboxylicanhydride unit in a solution of an amine in water or alcohols, such asmethanol or ethanol, or an organic solvent such as dimethylformamide, orby applying the foregoing solution by other means. While the reactionwill vary depending upon the class of amine used and the class of thereactive group of the membrane, generally speaking, a reaction time of 1minute to 48 hours at a temperature of 280 C. should be sufficient. Aconcentration of the amine in the solution of at least 0.01 percent, andpreferably 0.1-50 percent, is

'used.

When the acid amine bonds are formed at the surface of the startingmembrane or in the neighborhood thereof inclusive of the surface byusing a starting membrane in which the acid halide groups have beenintroduced as the reactive groups and reacting therewith a compoundcontaining at least one primary or secondary amino group, this compoundcontaining the amino group is consumed as a neutralizer as a result ofthe hydrogen halide that becomes liberated. Hence, if adehydrohalogenating agent is added to the foregoing reaction system, theconcentration in which the compound containing at least one primary orsecondary amino group is used can be conveniently reduced, since similarresults can be expected. On the other hand when the amount added of thedehydrohalogenating agent is insufficient, the compound containing theat least one primary or secondary amino group, which reacts with theacid halide group introduced into the starting membrane, is consumed asthe dehydrohalogenating agent. Hence, in general, thedehydrohalogenating agent is conveniently added in an amount of 0.01-40percent. As the dehydrohalogenating agent any of those known can be usedwithout any limitations whatsoever provided that they do not have anyadverse effects on the aforesaid acid amide conversion reaction. Asthese dehydrohalogenating agent, generally used with advantage are thecompounds having at least one tertiary or quaternary amino group and nothaving primary or secondary amino groups or the anion exchange solutionof the OH type or anion exchange resin of the OH type.

Further, for reducing the electric resistance of the cation exchangemembrane obtained in the present invention to a minimum, the presence inthe reaction system of at least one water-soluble salt selected fromgroup consisting of the salts of ammonium, and the alkali, alkalineearth and transition metals during the process of imparting the acidamide bond to the starting membrane is advisable, and especially goodresults are obtained when as the compound having the at least oneprimary or secondary amino group, as used in the present invention, ahigh-molecular weight member of said compounds, particularly a polymerhaving a molecular weight of above 300, e.g., polyethyleneimine,polyvinylamine, polyaminostyrene and polyallylamine, is used. And as theaforesaid metals, the following can be specifically indicated as beingmost favorably used in this case. As the alkali metals, convenient arelithium, sodium and potassium. As the alkaline earth metals, mention canbe made of such, for example, as magnesium, calcium, strontium andbarium. On the other hand, as the transition metals, included are thetransition metals belonging to groups IV and V of the periodic system ofelements, i.e., from Sc having the atomic number 21 to Zn having theatomic number 30 and from Y having the atomic number 39 to Cd having theatomic number 48. Further, there is no particular restriction as to theaforesaid at least one salt selected from those of ammonium and thealkali, alkaline earth and transition metals as long as they arewater-soluble salt. Usually usable are the inorganic salts such asnitrates, sulfates, sulfites, nitrites, halogenous salts, perhalogenoussalts, halides, oxyhalides and oxysulfates, and the organic salts suchas the aliphatic and aromatic carboxylates and sulfonates. It isbelieved that the addition of these water-soluble salts has thefollowing effects. in the case the water-soluble salt present is that ofammonium, an alkali metal or alkaline earth metal, the aforesaidcornpound, and particularly the polymer, of high molecular weight havingthe primary or secondary amino group contracts and becomes reduced inits volume to become fixed in this state in the starting membrane bymeans of the acid amide bond. On the other hand, when the water-solublesalt present is that of a transition metal, the aforesaid compoundhaving the amino group forms a chelate compound to become set in thestarting membrane in this drastically changed state by means of the acidamide bond. Hence, in this latter case, i.e., where a watersoluble slatof a transition metal is used, the compound having the primary orsecondary amino group, which is bonded by way of the acid amide bondremains in a state where it has formed a complex with the transitionmetal, with the consequence that it tends to be inferior in itspermselectivity of cations of smaller valence if used in this state.Thus, the foregoing complex is preferably decomposed before using themembrane. Since the decomposition of the complex can usually be readilyaccomplished by simply treating the membrane with an aqueous solution oflow pH, it merely suffices to wash or dip the membrane in an acidicsolution after it has been imparted the acid amide bonds. Further, ifthe amount added of the aforesaid water-soluble salt is too great, the

permselectivity between cations of the resulting cation exchangemembrane declines and hence is undesirable, whereas when the amount isinsufficient, fully satisfactory results are not demonstrated. Hence,usually the amount added of the water-soluble salts of ammonium, alkalimetals or the alkaline earth metals is conveniently a range of 0.1-2.5 N(normal), and preferably 0.5l.0 N, in the reaction system solution. Onthe other hand, water-soluble salts of transition metals areconveniently added in such a range that the mole ratio of the compoundhaving at least one primary or secondary amino group (PSAC) to thetransition metal, i.e., the mole ratio Me/PSAC, is 0.0030.15. (However,in the case where the PSAC is a polymer such as polyethyleneimine orpolyvinylamine, the mole ratio is that of the PSAC as a monomer unit tothe Me.)

In accordance with the invention method, the acid amide bond introducedmembrane is next treated with an aqueous alkaline solution to hydrolyzethe unreacted acid halide or carboxylic anhydride units to cationexchange groups. As the aqueous alkaline solution, usable are theaqueous solutions of caustic alkalis, such as caustic soda and causticpotash, or calcium and barium hydroxides. Thus a cation exchangemembrane having cation exchange groups of the alkali metal ion type oralkaline earth metal ion type is obtained. It goes without saying thatthis cation exchange membrane can be converted to an H-type cationexchange membrane by treatment with an aqueous solution of a mineralacid such as hydrochloric and sulfuric acids. If desired, the startingmembrane, after having been imparted the acid amide bonds, can be dippedin a solution of such as CH I, CH Br,

HCHO, BrC H,,Br or CHO l CHO,

thereby converting the free amino groups to tertiary or quaternarygroups.

As to whether or not the cation exchange membrane has the acid amidebonds can be confirmed qualitatively by the determination of thepresence of nitrogen by means of an elemental analysis of the resinpowder shaved from the surface thereof.

On the other hand, the quantitative measurement can be made in thefollowing manner. When the amount of acid amide bonds is great, it canbe computed from the difference in the ion exchange capacities betweenthe cation exchange membrane which has been imparted the acid amidebonds and a cation exchange membrane not so imparted. In the case wherethe amount of acid amide bonds is small, the determination can be madeby measuring the acid amide absorption band of the infrared absorptionspectrum analysis of the whole cation exchange membrane or the powderscraped off its surface by means of, say, steel wool. On the other hand,when a high-molecular-weight electrolytic substance such, for example,as polyethyleneimine or polyvinylamine, has been used as the compoundhaving at least one primary or secondary amino group, the decrease inthe concentration of the aforesaid highmolecular-weight electrolyticsubstance can be quantitatively measured by means of ultravioletabsorption of complex with transition metals. [For example, J. PolymerSci. 5 (8) l,l932,003 (1967).]

The method of using the invention cation exchange membrane is imposed noparticular restrictions, it being possible to use it in the usualelectrodialysis. For example, if the concentration of sea water iscarried out using the invention cation exchange membrane for selectivelyremoving the monovalent cations from among the cations of differentvalances, the monovalent ions contained in sea water can be selectivelyconcentrated. Further, when this is usually carried out on a commercialscale, the concentration using electrodialysis is best carried out byarranging such that a plurality of anion and cation exchange membranesare disposed in alternation.

For a more specific illustration of the present invention, the followingnonlimitative examples and comparisons are given.

In the examples and comparisons the electric resistance of the cationexchange membrane is a per unit area value obtained by using al,000-cycle alternating current in 0.5 N- NaCl solution of 250 C.

The transport number is that obtained when the electrodialysis wascarried out with a current density of 20 milliampere/cm. and 0.5 NNaClsolutions on both sides of the cation exchange membrane.

On the other hand. the permselectivity designated Tfifi was calculatedby means of the following equation from ratio of the transport number inthe membrane obtained by carrying out the electrodialysis with a mixedsalt solution of CaCl =0 .200 N and NaCl=0.200 N. The electrodialysiswas carried out in this case at 25 C. and a current density of 20milliampere/cm. with vigorous stirring of the solutions on both sides ofthe ion exchange membrane.

13 M1/ M2)/( M1/ M2) wherein t and t each represent the transportnumbers of cations M and M in the ion exchange membrane, and C and Ceach represent the concentrations of cations M, and M in the solutions.

Further, the pure salt ratio at the time of concentrating sea water wasobtained as follows:

pure salt ratio ([Na]+[K] )/[Cl] l00.

Further, the intramembranous ion exchange capacity of the cationexchange membrane was calculated on the basis of the followingexperiment. After three or four washings of a cation exchange membranealternately in l NHCl and 0.5 N- NaCl, it is washed four to five timesin l NHCl to effect a complete conversion of the cation exchangemembrane to the H-type. This cation exchange membrane is then thoroughlywashed in water until the methyl orange indicator does not turn red foreliminating the excess hydrogen ions. Next, this cation exchangemembrane is placed in pure water and its ion exchange capacity isdetermined by obtaining the titration curve with a pH meter using l/l0NNaOh. The cation exchange membrane whose measurements have beencompleted in this manner is again immersed in 0.5 NNaCl and brought toequilibrium, after which it is taken out, allowed to stand for 2 hoursin an C. air dryer and then returned to room temperature in adesiccator. This dried membrane is weighed, after which the ion exchangecapacity obtained above is divided by the membrane weight to obtain theion exchange capacity per 1 gram of dry membrane.

Further, the amount of acid amide bonds formed in the cation exchangemembrane obtained according to the present invention was determined bythe microanalytic method of quantitative analysis unless otherwiseindicated. For example, in the case of the invention sulfonic acid typecation exchange membrane imparted the acid amide bonds usingpolyethyleneimine, the amount of acid amide bonds is determined in thefollowing manner. To a fine powder scraped from the surface of theforegoing cation exchange membrane is added a great excess of aceticanhydride followed by refluxing for 2 hours. Next, the foregoing finepowder is separated by filtration and thoroughly dried under reducedpressure to completely remove the acetic acid and acetic anhydride. Theso obtained sample is submitted to infrared analysis by means of the KBrtablet method and the intensity ratio of the absorption peaks ofsulfonic acid amine and carboxylic acid amide is obtained. ln general,the absorption peak of sulfonic acid amide is observable at about 1,160cm. while the absorption peak of carboxylic acid amide which shiftsbetween l,740-l,630 cm. depending upon the class of the ion exchangemembrane usually appears in most cases at about 1,630 cm.

Next, benzenesulfonic acid amide and polyethyleneimine of known ratio ofprimary and secondary amino group content to the total amino group aremixed and dissolved in a solvent (ethyl acetate), following which agreat excess of acetic anhydride is added and refluxing is carried outfor 2 hours. The solvent and the unreacted acetic anhydride are thenremoved EXAMPLE 1 A pasty mixture of 95 parts of styrene, 5 parts ofdivinylbenzene, l parts of finely divided polyvinyl chloride, 25

under reduced pressure and a film is obtained. Three samples parts ofdioctyl phthalate and L5 parts of benzoyl peroxide in which the mixtureratio of the benzenesulfonic acid amide was applied to a polyvinylchloride cloth, which was then and the foregoing polyethyleneiminediffers are made into polymerized by heating at 110 C. for 4 hours toobtain a samples having the form of a membrane. These are submittedmembranous high-molecular-weight polymer 0.0 l 5 cm. in to infraredanalysis and calibration curves are plotted. On the thickness. Thedivinylbenzene which was of a purity of 5054 basis of these spectra, theamounts of sulfonic acid amide percent, wasamixture of o-, mandpdivinylbenzene, the rest bonded to all the primary and secondary aminogroups are calbeing ethyl benzene. (This is likewise also in thesubsequent culated. For example, astarting membrane of 130 cmF/(g. dryexamples.) Using the so obtained membranous high-molecumemb.), as usedin the hereinafter given example l, is used, lar-weight polymer as thestarting membrane, this was dipped and by operating as in example 2polyethyleneimine which is in a mixed solution consisting of 2 parts ofchlorosulfonic acid capable of being adsorbed in an amount of 2 mg./1OOcm? is of above 90 percent purity and 1 part of carbon tetrachloride,bonded to the starting membrane at or in the neighborhood of where thechlorosulfonatioh reaction was carried out for its surface. Since themolecular weight of -CH CH hours at 4-7C.The resulting chlorosulfonatedstarting mem- NH- is 43, the milliequivalent of the polyethyleneiminebrane was dipped in an aqueous or methanol solution containbecomes 2l/43)0.046 (meq./ 100cm?) at this time. Hence ing 5 percent of acompound indicated in table 1 having either the amount ofpolyethyleneimine which adheres per gram of a primary or secondary aminogroup under the conditions dry membrane be ome 0,046 (l 30/100=0 06 dspecified in table 1 to form the acid amide bonds in the surface memb.).However, the aforesaid polyethyleneimine contains 0f the membrane- Afterpl n of the foregoing reaction, the primary, eondary and tertiary aminogroups in the the starting membrane was immersed in aqueous l N-NaOHamounts of respectively 25, 50 and percent, and since the 25 Soluhoh for8 hours at room temperature to hydrolyze the primary and secondary a igroups hi h are bl f reacted chlorosulfone groups to cation exchangegroups. The forming the acid amide bond account for 75 percent of the 50Obtained C800" eXChange mbrane was then Washed total amino groups, theamount of the polyethyleneimine in thoroughly l NHC|, l NNacl and Waterthe Order the i amide bond becomes Q.()6) ]5=() 045 mach/(g given. Theinvention cation exchange membrane was thus obb th other h d h amount fid id bonded tained. The amount of the acid amide bonds and measurementas determined f the i frar d analysis f the powder results of the soobtained cation exchange membrane are scraped from the surface of theaforesaid cation exchange showhlh tab]? memhrane was Seen to be in aproportion f one to each fi Item No. l in table 1 has been given as acontrol. The results f the primary or Secondary amino groups as a resultf a given here are those of a cation exchange membrane obtaineddetermination using the calibration curve as explained in the asfollows: the Startmg membtahe has h t f h previously describedmicroanalytic method of quantitative fonated as the hetefnabovedescnbedexpenhteht, 15 analysis. Accordingly, the amount of acid amidebonded is me'dtatety tmmetseft m N N3OH Wtthout ""P the 0 45 X 1 5=0 0 9meq /(g| dry memh) which is about acid amide bonds, i.e., withoutreacting it with a compound 0.5 percent of the total ion exchangegroups, i.e., 1.82 havlhg the PmhaTy orisecohdal'y ammo p and this ismeq/(g dry memh lowed by the hydrolysis of the chlorosulfone groups.

TABLE I Reaction Compound solution used conditions Measurement resultsAcid Exchange Temamide Trans- Electric capacity perature Time bonds caport. resistance (maq./g.dry Number Solvent Class of compound 0.). (hr.)(percent) N. number (SI-cm!) member) 1 2. 6 0. 98 3. 5 1. 82 2Diethy1am1ne 25 6 9.9 1.6 0.98 10.3 1.64 3 Water..." Diethanolamine.-.25 10 7.6 1.3 0.92 10.0 1.68 4 Methanol Diphenylamine... 25 24 1.6 2.00.98 3.6 1.79 5 .d0. PhthalimidtL.-- 25 24 3.8 2.1 0.98 3.5 1.75 6Water.--" Piperazine 25 3 12.1 1.8 0.88 8.5 1.60 7 p-Aminosalicylic acid40 24 2. 2 1.5 0. 97 2.6 1. 78 8.. Do ecylamine 25 2 3.3 1.5 0.8810.5 1. 9 Tetraethylene pentamrne 25 8 3. 4 0. 9 0. 95 8. 0 1. 10- do.Triethylene tetramine- 25 5 7. 8 0. 7 0. 90 9. 5 1. 6 11. Methanolm-Phenylene diamin 25 24 12.6 0.6 0. 88 11. 0 1.5 12- Water..- Bismarckbrown 25 8 4.9 0.7 0.95 9.5 1. 13-.- v do. Auramine concentration"... 258 1. 6 1. 8 0.97 8.0 1. 7 14-.. .--.do..-.. Isonicotinic acidhydrazine-. 25 24 2. 2 1. 8 0.98 8. 0 1. 7 15 .do... Chrysoidinecrystals 25 8 1.1 2.0 0.98 3.5 1.8

The number of acid amide bonds in the case of the other EXAMPLE 2 aminescan also be determined by the same measurements method.

Again, the phosphoric acid amide bonds can also be calculated in likemanner. However, in the case of the carboxylic acid amide bonds, sincethe absorption intensity of carboxylic acid amide increases as a resultof the acetic anhydride treatment, the determination is best done fromthe calibration curve of carboxylic acid amide suitably plotted inadvance from the intensity ratio of carbonyl before and after the amidetreatment by means of carboxylic acid anhydride.

In the case of the hereinafter given example 1, the amount of acid amidebonded was calculated from the difference in the ion exchange capacitiesbetween the cation exchange membrane not imparted the acid amide bonds(No. l of table 1) and the cation exchange membrane imparted the acidamide bonds.

To a starting membrane 0.01 6-001 7 cm. in thickness as obtained inexample i were introduced chlorosulfone groups by operating as inexample 1. This starting membrane was immersed in aqueous 5 percentpolyethyleneimine (hereinafter abbreviated to PEI) for 16 hours at 25 C.to form acid amide bonds in the surface of the membrane. The membranewas then dipped in aqueous l NNaOH solution for 8 hours at roomtemperature, after which it was thoroughly washed as in example 1 toobtain a cation exchange membrane. The amount of acid amide bonds of theso obtained catioh exchange membrane and the results of the measurementof its T:,transport number and electric resistance are shown in table 2.As is apparent from table 2, the molecular weight of PEI had practicallyno effect, but when compared with the instance of the compounds used inexample 1 (table 1) itsTfi; is clearly superior.

TABLE 2 seawater used was adjusted to about 6 by the addition ofhydrochloric acid, except for the experiments Nos. 1, 2 and 8, in whichcase the usual as obtained sea water having a pH 8.2 Molecular electricwas used. Further, the results given for experiment No. 15 are "f cthose, given by way of comparison, of the instance where the of PE]amlde bonds TN: number ance (fl-c cation exchange membrane not havlngthe acld amlde bonds of example 1 (No. 1 of table 1) was used as thecation l 2000- 0.3 0.5 0.97 8.0 exchange membrane. 6000 10 From theresults glven ln table 3 lt ls obvlous that a marked 30.o00- 0.1 0.50.9a 8.0 enhanced of the pure salt ratio is demonstrated in the case23-3 where the invention cation exchange membrane has been used 6 3g;and further that the durability of the permselectivity of this cationexchange membrane is outstanding.

TABLE 3 Solvent and acid binder Pure PEI salt concen- Coneen- Electricratio tration tration Class resistance Transport (per- N umber (percent)(percent) (St-cm!) number cent) 7. 0 0. 98 97 10 7. 2 0. 98 96 5 M 5. 00. 98 95 5 10 no Pyridine solution 2.8 0.98 92 3 10 Pyridine-methanolsolution 2.3 0.98 91 3 10 aqTrimethylamine solution 5. 6 0. 98 92 3 10Trlmethylammeunethanol solution 3.8 0.98 93 3 10 aq Trlethenolaminesolution 7.3 0.98 93 3 10 no Monolauryl dimethylamine solution 6.8 0.9892 3 10 no B-diethylaminoethanol solution 6. 5 0.98 92 3 3Trim-octylamine" 5.8 0. 98 90 3 3 Tri-n-dodecylamine. 6. 2 0.98 88 3 2Amberlite IRA400* 5. 4 0. 98 90 3 2 Amberlite IR4B 5.0 0.98 89 3.0 0.9874 "A liquid anion exchange compound 0! the 0H type. Tradename of an OHtype anion exchange resin.

EXAMPLE 3 EXAMPLE 4 Chlorosulfone groups were introduced to a0.15-mm.-thick starting membrane as in example 2, following which theforegoing chlorosulfone groups were reacted for 16 hours at C. witheither an aqueous solution of a concentration indicated in table 3 ofPE1 having a molecular weight of 5,000 or a mixed solution containing adehydrohalogenating agent to form the acid amide bonds in the surface ofthe membrane. The chlorosulfone groups still remaining in the membranewere hydrolyzed with aqueous 1 NNaOH solution, followed by washing with1 N-HCl and 1 NNaCl to obtain a cation exchange membrane. Separately, apaste consisting of 50 parts of 2-methyl-5-vinylpyridine, parts ofstyrene, 6 parts of divinylbenzene, 15 parts of dioctyl phthalate, 65parts of finely divided polyvinyl chloride and 2 parts of benzoylperoxide was applied to Tevylon cloth (trade name of a cloth made frompolyvinyl chloride), after which Vinylon film (trade name of a clothmade from polyvinyl chloride), after which Vinylon film (trade name of afilm made from polvinyl alcohol) was intimately adhered to both sides ofthe foregoing cloth and polymerized by heating for 10 hours at 80 C.under pressure. The Vinylon film was then stripped and immersed for 24hours in a methyl iodide-gasoline (1:4) mixture, followed by thoroughwashing in methanol and further immersion for 12 hours at roomtemperature in 5 percent methanol solution of metaphenylene diamine.This was followed by dipping in a 37 percent formalin-hydrochloric acid(2:1) mixture to thus obtain an anion exchange membrane havingpermselectivity between anions.

A conventional multicompartment cell type brine concentration apparatuswas constructed using the foregoing anion and cation exchange membranes,and concentration of sea water was carried out continuously for a l-yearperiod. The average values of the results obtained for the periodbeginning 6 months after the start of the concentration operation to theend of the l-year period are shown in table 3. The pH of the A pastymixture was prepared by adding 100 parts of finely divided polyethyleneand 2 parts of benzoyl peroxide to a mixture consisting of parts ofstyrene, 10 parts of divinylbenzene and 25 parts of dioctyl phthalate.This paste was applied to a net made from polyethylene and polymerizedby heating for 4 hours at 1 10 C. to obtain a membranoushighmolecular-weight polymer. Using the so obtained membrane as thestarting membrane, the chlorophosphate groups were introduced thereintoby immersing it for 12 hours atroom temperature in a solution consistingof 25 moles of phosphorus trichloride and 1.2 moles of anhydrousaluminum chloride. After washing this membrane thoroughly with water, itwas dipped for 5 hours at room temperature in a methanol solutioncontaining 5 percent PEI to form the acid amide bonds. The membrane wasfurther dipped for 12 hours at room temperature in 1 N-NaOl-l to convertthe chlorophosphate groups to phosphorous acid groups to thus obtain acation exchange membrane. The percent phosphorous acid amide bonds ofthe so obtained cation exchange membrane was 0.05 percent. Further, itstransport number was 0.98, its resistance was 7.2 ohm-cm. and Ti}: was0.6. r

EXAMPLE 5 A starting membrane such as used example 1 was immersed for 8hours at 25 C. in a mixed solution consisting of 600 grams of CCl,,, 70grams of chloromethyl ether and 5 grams of SnCl with stirring, afterwhich it was thoroughly washed in methanol. This was followed byimmersing the membrane for 8 hours at room temperature in a mixedsolution concisting of 25 moles of phosphorus trichloride and 1.2 molesof anhydrous aluminum chloride. The following PEI treatment andsubsequent operations were then carried out as in example 4 cent, and ithad a transport number of 0.98, electric resistance of 6.9 ohm-cm. andT2: of 0.6.

EXAMPLE 6 A pasty mixture consisting of 95 parts of methacrylic acid,parts of divinylbenzene, 100 parts of finely divided polyvinyl chloride,25 parts of dioctyl phthalate and 1.5 parts benzoyl peroxide was appliedto a polyvinyl chloride cloth and polymerized by heating for 4 hours at110 C. to obtain a membranous high-molecular-weight polymer having athickness of 0016-0018 cm., which was used as the starting membrane.Dioctyl phthalate was removed from this membrane by immersing it inmethanol for 24 hours at room temperature. This was followed by dippingthe membrane for 5 hours at room temperature in a mixed solutionconsisting of 50 parts of phosphorus trichloride and 50 parts of carbontetrachloride to introduce the chlorocarboxylic acid group. Next, thismembrane was immersed for 12 hours at room temperature in a methanolsolution containing 5 percent PEI to form the carboxylic acid amidebonds in the surface portion of the membrane. The membrane was thendipped for 5 hours in water to convert the unreacted chlorocarborylicacid groups to carboxylic acid to obtain a cation exchange membrane. Thepercent carboxylic acid amides bonded to this cation exchange membranewas 0.2 percent and its transport number was 0.98, electric resistancewas 9.2 ohm-cm. and T5: was 0.4.

EXAMPLE 7 A styrene-divinylbenzene copolymer of less than 350 mesh wasobtained by the suspension polymerization of styrene and divinylbenzenein customary manner. This copolymer was dipped for 5 hours inchlorosulfonic acid of C. to introduce the chlorosulfone groups,following which 100 parts of the copolymer and 50 parts of finelydivided polystyrene were intimately mixed for 30 minutes at 1 10 C.using mixing rolls to form a 0.2-mm.-thick sheet. This sheet wasimmersed for 16 hours at 25 C. in a mixed aqueous solution containing 10percent PEI and 5 percent trimethylamine to form the sulfonic acid amidebonds in the surface of the sheet. This sheet was then dipped in lNNaOl-l solution to hydrolyze the unreacted chlorosulfone groups to thusobtain a cation exchange membrane (nonhomogeneous membrane) whosepercent acid amide bonds was 0.07 percent. The transport number of thiscation exchange membrane was 0.92, its electric resistance was 1.43ohm-cm. and T5; was 0.6.

EXAMPLE 8 A O.3-mm.-thick polyvinyl chloride sheet was immersed for 5hours at room temperature in a monomeric mixture consisting of 90 partsof styrene, 10 parts of divinylbenzene and 2 parts of benzoyl peroxide.The polyvinyl chloride sheet swelled by this immersion was thensandwiched between sheets of cellophane and polymerized for 4 hours at80 C. under pressure. The so obtained membranous high-molecularweightpolymer was used as the starting membrane. After introducing thechlorosulfone groups by dipping this membrane in 10 C. chlorosulfonicacid for 3 hours, it was immersed in an aqueous solution containing 10percent PEI and 5 percent triethanolamine to form the sulfonic acidamide bonds. This was followed by hydrolyzing the unreactedchlorosulfonic acid with l N--NaOH to obtain a cation exchange membranewhose percent sulfonic acid amide bonds was 0.5 percent. This cationexchange membrane had a transport number of 0.93, electric resistance of5.2 ohm-cm? and TE: of 0.4.

EXAMPLE 9 The sulfonation treatment of polystyrene was carried out at 95C. with the ratio ofpolystyrene to sulfuric acid of 1:10, followed byneutralization with sodium carbonate and thereafter dialyzed using acellophane membrane. Then trace amounts of salts were eliminated furtherby means of an ion exchange resin [Amberlite IRA-400 (trade name)]thereby obtaining pure sodium polystyrene sulfonate. A viscous solutionwas prepared by dissolving 10 parts of this sodium polystyrene sulfonateand 10 parts of polyvinyl alcohol in 20 parts of water. Next, thissolution was cast onto a sheet glass and was left standing to cause themoisture to evaporate. The resulting film was stripped from the sheetglass and immersed in a solution in 50 parts of water of 10 parts ofchloroacetaldehyde, 20 parts of sulfuric acid and 20 parts of sodiumsulfate, thus rendering the film insoluble in water. Next, afterthorough drying, this film was dipped in a mixed solution of 100 partsof chloroform and 50 parts of phosphorus pentachloride for 5 hours at 40C. to convert the sodium sulfonic acid groups to chlorosulfone groups.The sulfonic acid amide bonding operation and subsequent operations werethen carried out as in example 8 to obtain a cation exchange membranewhose transport number was 0.98, electric resistance was 3.0 ohm-cm. andwas 0.2. Further, the surface of this cation exchange membrane wasscraped off with steel wool and the presence of sulfonic acid amidebonds was confirmed by means of infrared analy- SIS.

EXAMPLE 10 After thoroughly drying sodium vinylsulfonate, 50 partsthereof was suspended in 150 parts of 05 C. chloroform, after whichparts of phosphorus pentachloride was added thereto. This was reactedfor 3 hours at 40 C. with thorough stirring, after which it was filteredand the chloroform in the filtrate was removed. The remaining liquid wasthen washed thoroughly in water to remove the phosphorus pentachloride.This was followed by adding ether and drying using calcium chloride,after which vacuum distillation was carried out adding hydroquinonethereby obtaining vinyl sulfonyl chloride. A mixture of 10 parts of thisvinyl sulfonyl chloride, 10 parts of styrene, 2 parts of divinylbenzeneand 5 parts of dioctyl phthalate was cast between a pair of sheetglasses and polymerized for 20 hours at 65 C. The membrane obtained inthis manner was immersed, as in example 8, in an aqueous solutioncontaining 10 percent PEI and 5 percent triethanolamine to impart thesulfonic acid amide bonds and thereafter hydrolyzed in 10 percent NaOHsolution for 6 hours at 85 C. to obtain a cation exchange membrane. Thepercent sulfonic acid amide bonds in this cation exchange membrane was0.38 percent, and its transport number was 0.98, electric resistance was3.0 ohm-cm. and was 0.25.

EXAMPLE 1 1 A pasty mixture consisting of parts of styrene, 5 parts ofdivinylbenzene, parts of polyvinyl chloride, 20 parts of dioctylphthalate and 2 parts of benzoyl peroxide was applied to a polyvinylchloride cloth, and this was then polymerized by heating, as in example1, to obtain a membranous highmolecular-weight polymer which was used asthe starting membrane. This membrane was submitted to a sulfonationtreatment for 12 hours at 60 C. using 98 percent concentrated sulfuricacid, and then converted to an Na type using 0.5 NNaCl. Using thissulfonated membranous highmolecular-weight polymer, it was dipped in amixed solution of 100 parts of chloroform and 50 parts of phosphoruspentachloride for 3 hours at 40 C. to convert the sulfonic acid groupsof the membrane to chlorosulfone groups. Thereafter, by operating as inexample 10 this membrane was converted to a cation exchange membranehaving sulfonic acid amide bonds. This cation exchange membrane had atransport number of 0.98, electric resistance of 7.4 ohm-cm? and of 0.4.

EXAMPLE 12 A pasty mixture was prepared by adding 80 parts of finelydivided polyvinyl chloride and 20 parts of chlorosulfonated polyethyleneto 100 parts of styrene, parts of divinylbenzene, 20 parts of dioctylphthalate and 2 parts of benzoylperoxide. This mixture was applied to apolyvinyl chloride cloth and polymerized by heating for 4 hours at 1 C.The resulting membranous high-molecular-weight polymer was thensulfonated by immersing in 98 percent concentrated sulfuric acid for 8hours at 60 C. The so obtained membrane was dipped in an aqueoussolution containing 5 percent PEI and 10 percent triethanolamine to formthe sulfonic acid amide bonds in the membrane, following which theunreacted chlorosulfone groups were hydrolyzed with l NNaOH solution toobtain a cation exchange membrane whose percent sulfonic acid amidebonds was 0.03 percent. The transport number of this cation exchangemembrane was 0.98, its electric resistance was 5.3 ohm-cm. and its Ti:was 0.6.

EXAMPLE 13 A styrene-butadiene copolymer latex (solids content 49chlorosulfonic acid and 1 part of carbon tetrachloride for 1 hour andintroducing the chlorosulfone groups thereinto, the operations as inexample 12 were carried out to convert the membrane into a cationexchange membrane having the sulfonic acid amide bonds. The transportnumber of the so obtained cation exchange membrane was 0.98 and itselectric resistance was 5 ohm-cm. and Tg: was 0.3.

EXAMPLE l6 A starting membrane obtained as in example i l was dipped in90 percent chlorosulfonic acid at 4 C. to introduce thereinto thechlorosulfone groups. Thereafter, by operating as in example 2 using thepolyvinylamine indicated in table 4 under the conditions indicatedtherein cation exchange membranes were obtained. The hydrolysis of themembrane forming the sulfonic acid amides was however carried out byimmersing the membrane in C. l NNaOH solution for 16 hours. Further, inthe case of experiments Nos. 2, 4, 5 and 7 of table 4, 10 percenttriethanolamine was added to a solution containing polyvinyl amine incarrying out the formation of the sulfonic acid amide bonds.

TABLE 4 Polyvinylamlne solution Reaction Results conditions Conoen-Percent Pure tration Temperacide Electric salt Experiment Molecular(weight ature Time amide resistance Transport ratio Number weightpercent) Solvent C.) (hr.) bonds (ll-cm?) number (per)- cent percent)containing 46 parts of styrene was applied to a cloth EXAMPLE 17 made ofglass fiber. On drying, a membranous high-molecularweight polymer wasobtained, which was used as the starting membrane. After dipping thismembrane in a solution containing a Friedel-Crafts catalyst (a solutionof 10 parts of anhydrous stannic chloride and 90 parts of carbontetrachloride) for 4 hours at 30 C., it was immersed for 2 hours in 10C. chlorosulfonic acid to introduce the chlorosulfone groups into themembrane. Thereafter, by operating as in example 8 a cation exchangemembrane was obtained. The transport number of this cation exchangemembrane was 0.98, its electric resistance was 7.2 ohm-cm. and its T5:was 0.52. The sulfonic acid amide bonds of the cation exchange membranewas confirmed by scraping the membrane with steel wool and analyzing thescraped material by means of infrared spectrum analy- SIS.

EXAMPLE 14 A 0.25-mm.-thick tetrafluoroethylene film was impregnatedwith styrene by dipping in 60 C. styrene. This film was then sandwichedbetween sheets of cellophane and polymerized by heating for 3 hours at80 C. to obtain a membranous highmolecular-weight polymer, which wasused as the starting membrane. By operating as in example 8 thismembrane was converted to a cation exchange membrane having the sulfonicacid amide bonds. The transport number of this cation exchange membranewas 0.96, its electric resistance was 8.7 ohm-cm. and its Tg; was 0.2.

EXAMPLE 15 A pasty mixture consisting of 96 parts of vinyltoluene(mvinyltoluene p-vinyltoluene 65:35), 4 parts of divinylbenzene, 100parts of polyvinyl chloride, l5 parts of dioctyl phthalate and 2 pans ofbenzoyl peroxide was applied to a polyvinyl chloride cloth andpolymerized by heating at 1 10 C. to obtain a membranoushigh-molecular-weight polymer, which was used as the starting membrane.After dipping this membrane in a 4 C. mixed solution consisting of 2parts of Example 16 was repeated except that a 5 (wt.) percent methanolsolution of polyallylamine having a molecular weight of 7,000 was usedinstead of the polyvinylamine, with the consequence that a sulfonic acidtype cation exchange membrane having the sulfonic acid amide bonds wasobtained. The percent sulfonic acid amide bonds of this cation exchangeresin was 0.32 percent, while its transport number was 0.98, itselectric resistance was 6.7 ohm-cm. and its pure salt ratio was 88percent.

EXAMPLE 18 A starting membrane obtained as in example ll was immersed ina mixed solution consisting of 2 parts of chlorosulfonic acid and 1 partof carbon tetrachloride and reacted for 2 hours at 10 C. to introducethe chlorosulfone groups into the membrane. After washing this membranethoroughly in sulfuric acids of 80, 40 and 20 percent concentrations, inthe order given, to remove the excess chlorosulfonic acid and car bontetrachloride, it was further washed thoroughly with water. The membranewas then dipped in a methanol solution containing 10 percent ofpolyaminostyrene (molecular weight 5,000) and 10 percent oftriethanolamine for 16 hours at 30 C., thus forming the sulfonic acidamide bonds in its surface. The unreacted chlorosulfone groups of thismembrane was then hydrolyzed with 1 NNaOH solution, after which themembrane was washed twice with l NHCl and 0.5 N NaOl-l in alternation,thus obtaining a cation exchange membrane. The electric resistance ofthis cation exchange membrane was 5.3 ohm-cm. while its transport numberwas 0.92 and pure salt ratio was 88 percent.

EXAMPLE l9 A starting membrane obtained as in example ll was sealed inwith a lzl gas mixture of S0 and Cl after which it was exposed toultraviolet rays for 8 hours to introduce the chlorosulfone groups intothe membrane. By operating as in examp1e7 this membrane was converted toa cation exchange membrane. The electric resistance of this membrancewas ohm-emf, its transport number was 0.98 and its was 0.5. Further,when the surface of the so obtained cation exchange membrane was scrapedoff with steel wool and submitted to infrared analysis, the presence ofthe acid amide bonds was confirmed.

EXAMPLE 20 A starting membrane obtained as in example 11 was immersed inC. fluorosulfonic acid for 4 hours, thus introducing the fluorosulfonegroup into the membrane. The membrane was then immersed in an aqueoussolution containing 10 percent PEI and 10 percent triethanolamine forhours at 18 C. to form the acid amide bonds. After hydrolyzing theunreacted fluorosulfone groups by dipping this membrane in 1 N-NaOH for16 hours, it was thoroughly conditioned with 1 NHC1 and 0.5 N-NaOHsolutions to obtain a cation exchange membrane whose transport numberwas 0.98, electric resistance was 7.7 ohm-cm. and T5: was 0.6.

EXAMPLE 21 A mixed solution obtained by adding 60 parts of dioctylphthalate to 80 parts of metacrylic acid and 20 parts of divinylbenzenefollowed by the further addition of 2 percent of benzoyl peroxide wascast between sheets of tetrafluoroethylene and polymerized for 5 hoursat 80 C. to obtain a membranous high-molecular-weight polymer, which wasused as the starting membrane. The membrane obtained in this manner,after having been removed of the dioctyl phthalate by reflux for 24hours with methanol, was dipped in a mixed solution consisting of 80percent of thionyl chloride and 20 percent of carbon tetrachloride for 8hours at 60 C. The membrane, after removal from the foregoing solution,was immediately immersed in a methanol solution containing 5 percent PEIand 10 percent triethanolamine where it was allowed to stand for 16hours, whereby the formation of carboxylic acid amide bonds took placein the surface of the membrane. The membrane was then introduced intowater to convert the unreacted chlorocarboxylic acid to carboxylic acidto thus obtain a cation exchange membrane whose transport number was0.98, electric resistance was 9 ohm-cm. and TN: was 0.4. In the case ofa cation exchange membrane which had not received the PE] treatment asin this experiment, i.e., did not have the carboxylic acid amide bonds,the transport number was 0.98, electric resistance was 7-8 ohm-cm. andTS: was 2.2.

EXAMPLE 22 Sixty parts of dioctyl phthalate and 2 parts of benzoylperoxide were added to parts of styrene, 50 parts of maleic anhydrideand 10 parts of divinylbenzene and the mixture, after being cast betweena pair of sheet glasses, was polymerized by heating for 5 hours at C.The membranous high-molecular-weight polymer obtained after removing thesheet glasses was used as the starting membrane. This membrane wasimmersed in an aqueous solution containing 10 percent PE] and 10 percenttriethanolamine for 10 hours at 60 C. to form the carboxylic acid amidebonds between the carboxylic acid anhydride units and PEI. The membranewas then dipped in 1 N-NaOH solution for 10 hours at room temperature tohydrolyze the unreacted carboxylic acid anhydride groups, after which itwas thoroughly washed in 1 N-HC1 and 0.5 NNaCl to obtain a cationexchange membrane. The transport number of this cation exchange membranewas 0.93 and its electric resistance was 8.1 ohm-cm. 2 and was 0.4.

EXAMPLE 23 To a highly viscous solution obtained by dissolving 30 gramsof polyvinyl acetate in a mixture of 90 parts of methacrylic 56d, 10parts of divinylbenzene and 30 parts of maleic anhydride were furtheradded 2 parts of benzoyl peroxide and 25 parts of dioctyl phthalate.This solution was applied to a polyvinyl alcohol cloth and polymerizedby heating as in example 21 to obtain a membranous high-molecular-weightpolymer. This membranous polymer from which dioctyl phthalate wasremoved by refluxwith a methanol solution for 24 hours was used as thestarting membrane. By operating thereafter as in example 21 a cationexchange membrane having the carboxylic acid amide bonds was obtainedfrom the foregoing starting membrane. The transport number of thiscation exchange membrane was 0.92, its electric resistance was 12.32ohm-cm. and its T5: was 0.6.

When the surface of this cation exchange membrane was scraped off withsteel wool and the infrared analysis was carried out, the carboxylicacid amide bonds were confirmed at the absorption band of 1,635 cmf.

EXAMPLE 24 The membranous high-molecular-weight polymer obtained as inexample 11 was used as the starting membrane and chlorosulfone groupswere introduced into this membrane by operating the chlorosulfationreaction as in example 1. This membrane was then immersed at roomtemperature in 98 percent concentrated sulfuric acid for about 10minutes and subsequently in successively diluted sulfuric acids of 80,60, 40 and 20 percent concentration for periods of about 10 minutes eachin the sequence given, after which it was finally dipped in cold water.This was followed by immersing this membrane in a mixed aqueous solutionof the composition indicated in table 5 for 16 hours at room temperatureand removing the unreacted foregoing mixed aqueous solution bywaterwashing to obtain a membrane having sulfonic acid amide bonds inits surface. This membrane was then dipped in aqueous 2.5 N NaOHsolution for 10 hours at room temperature to convert the unreactedchlorosulfone groups to sulfonic acid groups to thus obtain a cationexchange membrane. This cation exchange membrane was washed repeatedlyin 0.5 N-NaC1 and 1 NHC1 in alternation for three times and finallydipped in 0.5 N-NaCl solution. When the so obtained cation exchangemembrane was measured for its transport number, electric resistance andpure salt ratio, the results. were as shown in table 5. In table 5 thesalt indicated as Ph(OH)COONa under item No. 10 is an abbreviation of CH (OH)COONa.

TABLE 5 Composition of mixed aqueous solution Results Amine compoundsAcid Binder Salt Added ure Concen- Concensalt Electric tration trationConcenratio resist- (per- (pertratlon (per- Transport ance cent) Classcent) Class (N) cent) number (tZ-cmfi) 5 NaCl 1 93 0. 98 3. 5 5 NaCl 191 0.97 4. 5 3 TEA 10 NaCl 2.5 0. 98 3.5 3 TEA 10 021012 0. 1 92 0.98 4.5 3 TEA 10 LiCl 0. 5 94 0. 98 3. 5 3 TEA 10 LiCl 1.0 98 0. 98 2.5 3 TEA10 MgSO4 0. 1 92 0. 97 4. 0

transition metal, as indicated in table 6, instead of the mixed aqueoussolution used in example 24 was treated as in said ex- TABLE 5 ContinuedComposition of mixed aqueous solution Results Amine compounds AcidBinder Salt Added P ure Concen- Concensalt Electric tration trationConcenratio resist- Molecular (per- (pertration (per- Transport aneeNumber weight Class cent) Class cent) Class (N) cent) number (SZ-cmfl)3" TEA 5 KNO; 0.5 90 0.98 3.5 3 TEA 5 NazSOa 0. 2 92 0. 97 3. 3 TEA 5Ph(OH)COONa 0. 5 90 0.98 4. 0 3 TEA 5 CoHaSOaNa 0. 5 89 0.98 3. 8 3 TEA5 NHtCl 0. 3 93 0. 98 4. 2 5 TEA 8 NaCl 1 94 0. 97 1. 9

EXAMPLE 25 A is the number of acid amide bonds per gram of dry mem- Astartin membrane re ared as in exam le 24 but usin a brane and g p p p gB is the number of cation exchange groups per gram of dry mixed aqueoussolution containing a water-soluble salt of a membrane said acid amidebonds being composed of a cation exchange group and an amine having oneamino group containing at f l f p 3 Canon exghange gifib fi E 3 leastone hydrogen atom bonded to a nitrogen atom. 2 exc r i i gi f :2 g 2.The cation exchange membrane of claim 1 wherein said b d or 2 d th no f2 cation exchange group is selected from the class consisting of on gwas was 3 a e i T a e sulfonic acid, carboxylic acid and phosphonic acidgroups. s i e gi num e ec i 2? 25 3. The cation exchange membrane ofclaim I wherein said i R ratflo g g g 5525. 2 m acid amide bonds areselected from the group consisting of ts Co 0 n ta e Mel m 6 sulfonicacid amide, carboxylic acid amide and phosphoric mole ratio of thetransition metal (Me) to the polymer having acid amida a Pnmary orSecondary m group (PSAC)' the mole: 4. The cation exchange membrane ofclaim 1 wherein said being that per monomer unit OfIPS/TC. For example,m the amine has a molecular weight ofat least 200 case of a Valueexpresse as t 6 mo e who per 5. The cation exchange membrane of claim 4wherein said r amine is selected from the group consisting of compoundsof CHT"CH2 NH the formula Further, the following abbreviations have beenused in table 6. E R6 H MLDMA denotes monolauryl dimethylamine; TOAn-tri-ocf I tylamine; IRA, Amberlite IRA-400 (trade name), an OH-type nanion exchange resin; and BSCO, cobalt benzenesulfonate. R4 R;

TABLE 6 Composition of mixed aqueous solution Water-soluble transi-Polymer having amino group Acid binder tlon metal salt Results Concen-Coucen- Pure Trans- Electric Molecular tration tration Mel salt ratioport resistance weight Class (percent) Class (percent) Class PSAC(percent) number (Q-cm!) 40,00060,000 PEI 10 CuSOi 0.013 94 0.93 4.240,000-60,000 PEI 5 TEA 10 ZnSO4 0.05 95 0.98 3.8 5,000 PVA 5 TEA 5011504 0.02 93 0.98 4.5 40, 00060,000 PEI 5 TEA 10 CuSO4 0.016 94 0.984.5 40,000-60, 000 PEI 5 TEA 10 011504 0. 125 85 0. 98 3. 5 40,GOO-60,000 PEI 5 TEA 10 FezSOa 0.008 93 0.98 5.0 40, 00060,000 PEI 5 TEA10 Fe2SOa 0.017 94 0.98 4.2 40000-00000 PEI 5 TEA 10 msot 0.03 91 0.98as 40, 000-60, 000 PEI 3 TEA 10 COClz 0. 008 94 0. 98 4. 8 40000-60000PEI 5 TEA 10 00012 0.017 92 0. 98 4.2 40,00060,000 PEI 5 TEA 10 000120.033 89 0. 98 3.5 5,00010,000 PEI 7 TEA 10 TiOSO4 0.03 91 0.98 3.95,00010,000 PEI 7 TEA 10 K2CrO4 0.025 89 0.98 3.9 5, 00010,000 PEI 7 TEA10 ZrOClr 0.03 93 0.98 3.9 5,000-10,000 PEI 7 TEA 10 cdsoi 0.010 04 0.984.3 40,000-60,000 PEI a Pyridine 10 011804 0. 0s 93 0.98 4.040,00060,000 PEI 5 MLDMA 5 CuSO4 0.03 92 0.98 4.3 40,000-650,000 PEI 5'IOA 3 CuSO4 0.02 94 0.9 3.8 40,000-60,000 PEI 5 IRA 1 20 CIISOA 0.02 910. 98 4.0 40,000-60,000 PEI 5 TEA 10 CHBCOOCH 0.05 94 0.98 4.3 40,00060,000 PEI 5 TEA 10 B800 0.04 91 0.98 4.0

We claim:

1. A cation exchange membrane comprising a membranous insoluble,infusible organic high molecular weight polymer having cation exchangegroups chemically bonded thereto and having the dimension of at least icentimeter in two directions, a substantial portion of the surface ofsaid membrane being chemically bonded with acid amide bonds in aproportion such that the percentage indicated by the following equationis satisfied:

wherein wherein R R and R are each selected from the group consisting ofhydrogen, alkyl and aryl, R and R are each alkylene, and n is a numberfrom 0 to l or more; and polymers having the repeating unit of theformula wherein R is selected from the group consisting of hydrogen andalkyl, R, is selected from the group consisting of alkylene andphenylene, and m is a number from to l.

6. The cation exchange membrane of claim 1 wherein said amine ispolyethyleneimine.

7. The cation exchange membrane of claim 1 wherein said amine ispolyvinylamine.

8. The cation exchange membrane of claim 1 wherein said amine ispolyaminostyrene.

9. The cation exchange membrane of claim 1 wherein said amine ispolyallylamine.

10. A method of making a cation exchange membrane having chemicallybonded cation exchange groups and acid amide groups which comprisesreacting an amine having at least one amino group containing at leastone hydrogen atom bonded to a nitrogen atom, with an insoluble,infusible organic high molecular weight polymeric membrane havingchemically bonded thereto reactive groups selected from the groupconsisting of sulfonic acid halide groups, carboxylic acid halide groupsphosphoric acid halide groups and carboxylic acid anhydride units, in aproportion such that the percentage indicated by the following equationis satisfied:

A/(A+B)Xl0(h[.l5-l0 ]l l0 to 15% wherein A is the number of acid amidebonds per gram of dry membrane, and B is the number of cation exchangegroups per gram of dry membrane, and thereafter treating said membranewith an aqueous alkaline solution to hydrolyze the remaining reactivegroups to cation exchange groups.

11. The method of claim 10 wherein a water-soluble salt of a cationicconstituent selected from the group consisting of ammonium, alkalimetals, alkaline earth metals and transition metals is present duringthe reaction of said membrane having reactive groups with said amine.

' UNITED STATES PATENT OFFICE CERTIFICATE 0F CORRECTION Patent No. 3,647 O86 Dated March 7 1972 Inventor(s) NI ET AL It is certified thaterror appears in the above-identified patent and that said LettersPatent are hereby corrected as shown below:

Page 5, column 10, delete the formula between lines 21 and 23 and insertm2 T ml m2 m1 m2 g in Table 3, Number 10, after "aq", delete ''B" andinsert Page ll, in Table 6, 3rd entry under the heading Electricresistance.

delete "4. 5" and insert 4. 0

Page 11, in Table 6, 9th entry under the heading Concentration (Z)delete "3" and insert 5.

Page 11, in Table 6, 18th entry under the heading Transport Number,

delete "0.9" and insert O. 98

Signed and sealed this L th day of July 1972.

(SEAL) Attest:

EDWARD I LFLETCHER, JR ROBERT GOTTSGHALK Attesting Officer Commissionerof Patents FORM PO'wBO He's-3) USCOMM-DC soamaes "I U 5, GOVERNMENTPRINTING OFFICE: I969 0*366-334

2. The cation exchange membrane of claim 1 wherein said cation exchangegroup is selected from the class consisting of sulfonic acid, carboxylicacid and phosphonic acid groups.
 3. The cation exchange membrane ofclaim 1 wherein said acid amide bonds are selected from the groupconsisting of sulfonic acid amide, carboxylic acid amide and phosphoricacid amide.
 4. The cation exchange membrane of claim 1 wherein saidamine has a molecular weight of at least
 200. 5. The cation exchangemembrane of claim 4 wherein said amine is selected from the groupconsisting of compounds of the formula
 6. The cation exchange membraneof claim 1 wherein said amine is polyethyleneimine.
 7. The cationexchange membrane of claim 1 wherein said amine is polyvinylamine. 8.The cation exchange membrane of claim 1 wherein said amine ispolyaminostyrene.
 9. The cation exchange membrane of claim 1 whereinsaid amine is polyallylamine.
 10. A method of making a cation exchangemembrane having chemically bonded cation exchange groups and acid amidegroupS which comprises reacting an amine having at least one amino groupcontaining at least one hydrogen atom bonded to a nitrogen atom, with aninsoluble, infusible organic high molecular weight polymeric membranehaving chemically bonded thereto reactive groups selected from the groupconsisting of sulfonic acid halide groups, carboxylic acid halide groupsphosphoric acid halide groups and carboxylic acid anhydride units, in aproportion such that the percentage indicated by the following equationis satisfied: A/(A B) X 100 (15- 10 5) 1 X 10 5 to 15% wherein A is thenumber of acid amide bonds per gram of dry membrane, and B is the numberof cation exchange groups per gram of dry membrane, and thereaftertreating said membrane with an aqueous alkaline solution to hydrolyzethe remaining reactive groups to cation exchange groups.
 11. The methodof claim 10 wherein a water-soluble salt of a cationic constituentselected from the group consisting of ammonium, alkali metals, alkalineearth metals and transition metals is present during the reaction ofsaid membrane having reactive groups with said amine.